In laser welding, two joined portions of workpieces to be joined are irradiated with a laser beam, so that the workpieces in the irradiated portion melted and joined by energy of the laser beam. Laser welding permits rapid welding because physical contact with a workpiece is not needed. Furthermore, since a laser beam has high energy density, the laser welding permits welding in a state in which influence of heat is limited to a narrow range of a workpiece.
On the other hand, in the laser welding, a bead width that is a region to be welded is narrow. Accordingly, tolerance to deviation from a target of a laser beam is small, and accuracy of a portion to be irradiated with the laser beam in a workpiece is required. Bad accuracy of the portion to be irradiated with the laser beam in the workpiece tends to cause defective fusing due to deviation from the target of the laser beam. In order to cope with this problem, the following methods are known.
For example, PTL 1 describes a laser welding method including forming a V-shaped bevel groove in a workpiece in advance, and irradiating the V-shaped bevel groove with a laser beam. PTL 2 describes a laser welding method of carrying out helical scanning by a laser beam. PTL 3 describes a laser welding method in which rotating scanning by a laser beam is carried out so as to draw a circular or elliptical locus.